Fossil Record 19(1): 61-81, doi: 10.5194/fr-19-61-2016
Scale morphology and specialized dorsal scales of a new teleosteomorph fish from the Aptian of West Gondwana
expand article infoP. G. Giordano, G. Arratia§, H.-P. Schultze§
‡ Universidad Nacional de San Luis, Chacabuco 917, San Luis, CP: 5700, Argentina§ Biodiversity Institute, Natural History Museum, The University of Kansas, Dyche Hall, Lawrence, Kansas 66045–7561, United States of America
Open Access
Scales of a new species of Teleosteomorpha from the continental Aptian ofthe south of South America are studied. These neopterygians are from the LaCantera Formation in central Argentina, and were previously identified asPholidophoriformes. They present ganoid scales; most of them are rhombicwith well-developed peg-and-socket articulations and possessing a smoothsurface. They have a straight posterior margin, but occasionally, somescales of the flank have a sinuous posterior margin with one or twoserrations. The shape of the scales varies along the body from large,rectangular and deeper than long scales behind the head to the preanalregion to smaller and rhomboidal scales in the caudal region. There are afew horizontal rows along the flank and about 32 lateral line scales. Thick,round ganoid scales are present in the prepelvic region close to the ventralmargin. The round and rhombic scales present growth lines, which formconcentric ridges on the external side. A characteristic row of deep scalesforms the dorsal margin on each side of the body; a row of median ridgescales is not present. This is a unique feature of the studied fishes.Scutes covered with unornamented ganoine precede the pelvic, dorsal, andanal fins, as well as the dorsal and ventral margins of the caudal fin. Theposterior margin of the dorsal lobe of the caudal fin is formed by a singleline of scales, which continues and covers the base of the first principalcaudal ray. Histological studies reveal a lepisosteoid-scale type withmultiple ganoine layers, lack of dentine, and the presence of canaliculi ofWilliamson. The macro- and micromorphology of the scales shows features thatare found in other teleosteomorphs, but also in other neopterygians.